The Third Generation Partnership Project (3GPP) produces standards that govern aspects of known mobile communications systems, such as the system known as Long Term Evolution (LTE). In Release 12 of technical specification TS 23.303, the 3GPP specifies functionality called Proximity-based Services (ProSe). This functionality includes methods that enable User Equipment (UE) to communicate directly with one another, UE to UE, by using a new radio channel (D2D—direct UE to UE radio channel for ProSe) based on LTE technology; i.e. communication between two or more UEs in proximity that are ProSe-enabled, by means of user plane transmission using Evolved Universal Terrestrial Radio Access (E-UTRA) technology via a path not traversing any network node.
Before a UE can start to use the ProSe services, the UE needs to reach ProSe Functions/Servers (PFs) in the LTE Evolved Packet Core (EPC) network in order to obtain authorization. This presents problems, as are described in the following.
PFs can be located in a number of places: There may be a PF in the home Network (NW), in the visited NW (if the UE is roaming), and in local NWs (i.e., in the vicinity of the UE). A local NW is an NW which is not the serving NW of the UE, and in whose radio resources the UE is authorized by the home NW to engage in so called ProSe Direct Discovery, which is a procedure employed by a ProSe-enabled UE to discover other ProSe-enabled UEs in its vicinity by using only the capabilities of the two UEs with E-UTRA technology.
The 3GPP specifies UE-to-PF-signalling over the user plane. In general, the UE is not aware of whether a Packet Data Network (PDN) Connection is home-routed or whether it is a Local Break-Out (LBO); that is, the routing of roaming traffic that is handled by a local operator without going back to the home NW. The signalling from user to NW through the Internetwork Packet Exchange (IPX) across NW borders requires tunnelling and extensive configuration and should be avoided. Also, setting up a new home-routed PDN connection should be avoided if possible. The reason is because of the limit on the number of PDN connections that can be set up (e.g., three connections in some NWs) and the limited number of bearers (up to eight).